Abstract: The microstructures and properties of four different status of 10 CrNi5 MoV steel including as-received sample, stress relieving heat treatment sample without plastic deformation, 6.6% plastic deformation sample and stress relieving heat treatment sample with 6.6% plastic deformation were investigated. The results indicated that after stress relieving heat treatment, the compressive yield strength of the 6.6% plastic deformation sample increased significantly, meanwhile, the Bauschinger effect was eliminated. The impact absorbed energies at-20 ℃ and-84 ℃ decreased by 39 J and 42 J, respectively, and embrittlement of the material occurred. The microstructures and grain sizes had no obvious differences before and after stress relieving heat treatment. It also found that strip-shaped carbide was formed between martensitic laths in the stress relieving heat treatment sample of plastic deformation and the segregation of phosphorus, nickel, carbon and other elements at grain boundaries happened, which contributed to the embrittlement of the stress relieving sample with plastic deformation.